Temperature ratings were designed to give an idea of a sleeping bag’s performance. For many years, however, they became an area subject to marketing abuse. Recent efforts have been made to restore their validity.
There is no global standard for measuring sleeping-bag performance. Instead, there are several national norms and one European standard:
| UK | BS 4785 |
| France | NF G08-013 |
| Europe | EN 13537 |
| Norway | Thelma |
| USA | ASTM F1720 |
In 2005 the European Standard EN 13537 became the official standard for the labelling of sleeping bags in the European Community. The standard is not mandatory, so brands are not legally required to comply (for the moment).
Most brands have, however, agreed to follow the EN13537 standard, although not necessarily to full compliance (which includes labelling information on fabrics and filling as well as on temperature values). The minimum standard recommended by the European Outdoor Group (the outdoor trade organisation) is the labelling of temperature values as shown in the table below:
| EN13537 Upper limit |
Highest temperature at which a standard adult male is deemed to have a comfortable night’s sleep without excessive sweating |
| EN13537 Comfort |
Temperature at which a standard adult female can have a comfortable night’s sleep |
| EN13537 Lower limit |
The lowest temperature at which a standard adult male is deemed able to have a comfortable night’s sleep |
| EN13537 Extreme |
A survival rating only for a standard adult female. After 8 hours, hypothermia may start to start set in. |
At Lightwave, it is our opinion that the Upper Limit and Extreme figures are of not much value. Consequently, we quote the Comfort and Lower limits only. The EN13537 values are quite conservative, but we do feel they accurately reflect the temperature limitations of the sleeping bag for a comfortable night’s sleep. Obviously, individual tolerances may allow some people to go beyond these figures, but we believe this is at the discretion of the user and is not something to be claimed by us.
The EN13537 test uses a mannequin that radiates heat. It is clothed with a simple base layer and placed in a sleeping bag in a chamber maintained at a constant temperature. The mannequin is heated until it has reached a stable surface temperature of 34ºC (human skin temperature). The amount of energy required to maintain this surface temperature is then measured, and the thermal resistance (i.e. insulation) is calculated.
Naturally, the idea of the test is to duplicate real-use conditions. However, like all other similar tests, it fails on several counts. First, it relies on parameters for a “standard” male and female – which would be more useful if means showing how we could each measure our personal degree of deviation from “standard”, and the impact or significance of these, were published. Second, our own “standard” condition varies from one day to the next depending on physiological and environmental conditions. Thirdly, the test gives temperature values at which the standard person will be “comfortable” – a concept that is impossible to quantify for any individual.
Another shortcoming of the EN13537 test lies in its use of a mannequin. Bags that are smaller and fit the mannequin more snugly will return better test results than a larger, more generously sized sleeping bag. So whilst the EN standard may attempt to create a “real-world” test of performance, the best it can achieve is a basis of comparison against competing products, and even then such comparisons can be distorted.